The present invention pertains to the technical area of air heat exchangers and finds application in the sphere of heat exchangers in their general meaning.
The subject of the invention more particularly concerns the metal fins used in heat exchangers, mechanically assembled to tubes to form indirect transfer surfaces intended to increase the heat exchange surface areas between firstly tubes in which a first cold or hot liquid circulates and secondly a second fluid such as air which circulates between the tubes and along the surfaces of the fins in a determined flow direction.
These fins are generally made in the form of plates arranged parallel to each other and spaced apart over a determined pitch in relation to the intended application. Tubes pass through these fins to which the fins are crimpled via a mechanical or hydraulic process.
For dry surface exchangers, the global coefficient of heat transfer chiefly depends on air velocity, the ratio of the airside and fluid side surface areas, and on the efficacy of the fins. An efficient fin translates as an airside thermal resistance that is as low as possible (or an airside heat transfer coefficient as high as possible) whilst having the lowest possible air pressure loss.
In the prior art, various forms of embodiment of fins are known. One first known type is a fin in the form of a planar plate. This planar fin has the advantage of having very low pressure drop. However, the disadvantage of this planar fin is its very strong airside thermal resistance.
To overcome the low heat exchange capacity of the planar fin, it is known to have recourse to so-called louvered fins, comprising fixed inclined slats spaced apart by openings allowing the air to pass. The advantage of the louvered fin is its low airside thermal resistance. However, the louvered fin has very high pressure drop and can undergo heavy fouling on account of its geometry.
A so-called patterned slat is also known comprising corrugations in the direction of the air flow. The profile of these fins generates zones of turbulence, vectors of strong heat transfer, but also dead zones in the proximity of the tubes where heat transfers are much lower. A variant of this embodiment is illustrated by U.S. Pat. No. 4,434,846 which sets out to guide air in the direction of the tubes, which leads in particular to a pressure loss.
Analysis of known fins leads to ascertaining that the various variants of embodiment of means to increase heat exchanges between the air and fins are not satisfactory in practice.